METHODS OF DIAGNOSIS 473 



that a picture is presented which is obtained in no other con- 

 dition, and a microscopic examination may be sufficient for 

 practical purposes. According to Koch, a diagnosis was made 

 in 50 per cent, of the cases during the Hamburg epidemic by 

 microscopic examination alone. In the case of the first appear- 

 ance of a cholera-like disease, however, all the other tests 

 should be applied before a definite diagnosis of cholera is made. 

 Dunbar has recently introduced a method for rapid diagnosis 

 which depends on the properties of an anti-cholera serum. Two 

 hanging-drop preparations are made, each consisting of a small 

 portion of mucus from the suspected stool broken up in peptone 

 solution. To one a drop of a 50-fold dilution of normal serum 

 is added, to the other a drop of a 500-fold dilution of an active 

 cholera serum. If the spirilla present are cholera organisms, 

 they retain their motility in the first preparation, while they lose 

 it and then become agglutinated in the second. By this method 

 a diagnosis may sometimes be given in a few minutes. (It 

 should be kept in mind that some strains are not agglutinable 

 by a given anti-cholera serum : this seems to be especially the 

 case when the organisms have resided for some time in the human 

 body that is, in convalescents and carriers.) 



If the organisms are very numerous, gelatin or agar plates 

 may be made at once and pure cultures obtained. 



If the spirilla occur in comparatively small numbers, the best 

 method is to inoculate peptone solution (1 per cent.) and incubate 

 for from eight to twelve hours. At the end of that time the spirilla 

 will be found on microscopic examination in enormous numbers 

 at the surface, and thereafter plate cultures can readily be made. 

 If the spirilla are very few in number, or if a suspected water is 

 to be examined for cholera organisms, the peptone solution 

 which has been inoculated should be examined at short intervals 

 till the spirilla are found microscopically. A second flask of 

 peptone solution, should then be inoculated, and possibly again 

 a third from the second, and then plates may be made. In such 

 circumstances Dieudonne's medium (p. 44) has been found of 

 much service. For the separation of the organism Ottolenghi 

 has introduced a medium composed of ox-bile to which 3 per 

 cent, of a 10 per cent, solution of sodium carbonate is added : it 

 is sterilised in the autoclave. It is used in the same way as 

 peptone solution, and the advantage claimed for it is, that it in- 

 hibits the growth of most intestinal bacteria ; on the other hand, 

 the cholera organism appears to grow rather less rapidly than in 

 peptone solution. 



When a spirillum has been obtained in pure condition by 



